SOP: Calibration of Pressure Transducer

1. Purpose

To define the standard procedure for zero and span calibration of the pressure transducer using a pressure calibrator, ensuring accurate and stable measurement output.

2. Scope

This procedure applies to all pressure transmitters of this model that provide potentiometer-based zero and span adjustment.

3. Tools Required

• Pressure calibrator (hand pump / deadweight / electronic calibrator)

• Suitable screwdriver (small, flat)

• Spanner or wrench (for loosening plug nut)

• Multimeter or loop calibrator (if required for output verification)

4. Preconditions

• ✅ The transmitter must be powered ON

• ✅ The transmitter must be allowed to warm up for at least 30 minutes to reach operating temperature

• ✅ The transmitter must be connected to a pressure calibrator

• ❌ Do NOT attempt calibration without a pressure calibrator (this is not a guessing game)

5. Safety & Important Notes

• Calibration can only be done using a pressure calibrator.

• Zero and Span adjustments are done via internal potentiometers.

• The transmitter is sealed using potting compound. The compound reseals itself after adjustment — no drama.

6. Identification of Parts (As per Drawing)

• ① Plug nut – Must be loosened

• ② Potting compound access point

• ③ Zero adjustment potentiometer (±10% approx)

• ④ Span adjustment potentiometer (±20% approx)

7. Calibration Procedure

Step 1: Preparation

1. Connect the pressure calibrator to the pressure port of the transmitter.

2. Power ON the transmitter.

3. Wait minimum 30 minutes for temperature stabilization.

Step 2: Open Access to Adjustment

1. Loosen and unscrew the plug nut (①).

2. Insert a screwdriver through the potting compound (②) to reach the potentiometers.

Step 3: Zero Adjustment

1. Apply 0% pressure (or LRV) using the pressure calibrator.

2. Adjust the Zero potentiometer (③) until output matches:

   • 4.00 mA (for 4–20 mA) or

   • 0 V / correct digital value (as applicable)

3. Zero adjustment range is ±10% approx

Step 4: Span Adjustment

1. Apply 100% pressure (or URV) using the pressure calibrator.

2. Adjust the Span potentiometer (④) until output matches:

   • 20.00 mA (for 4–20 mA) or

   • Full-scale output value

3. Span adjustment range is ±20% approx

Step 5: Iteration (Important)

1. Recheck Zero

2. Recheck Span

3. Repeat steps 3 and 4 until both zero and span are correct

(Yes, this back-and-forth is normal. Welcome to the real world.)

Step 6: Sealing

1. Remove the screwdriver.

2. The potting compound will self-close the access hole.

3. Tighten the plug nut (①) properly.

8. Final Verification

• Check output at:

  • 0%

  • 25%

  • 50%

  • 75%

  • 100%

• Ensure output is linear and within tolerance.

9. Acceptance Criteria

• Zero and span match specified values

• Output is stable and repeatable

• No leakage from plug or pressure port

10. Common Mistakes

• ❌ Calibrating without warm-up

• ❌ Adjusting span before zero

• ❌ Not looping back to recheck zero after span

• ❌ Using a screwdriver like you’re tightening a truck wheel